Rotary extrusion-blow moulding machine with tilting moulds

ABSTRACT

An extrusion blow-molding machine, including several molding units borne by a carrousel rotating about a substantially vertical axis (A 1 ), wherein each molding unit is mounted on the carrousel such that it can be tilted about a substantially horizontal axis (An).

BACKGROUND OF THE INVENTION

The invention concerns a rotary extrusion/blow-molding machine.

More particularly, it concerns machines provided with several moldingunits carried by a carrousel that is rotatable around an appreciablyvertical axis. In a known way, each molding unit has a two-part mold,both parts being movable with respect to each other between an openposition and a closed position.

These machines also have an extrusion head that is placed above thecarrousel in a specific angular position around the carrousel's axis ofrotation.

Each mold is controlled to be in the open position when thecorresponding unit is located below the extrusion head, and to closeagain after having seized a section of preform flowing from theextrusion head.

The invention is applicable more particularly in the case of machines inwhich each molding unit is mounted on the carrousel in a way that ismovable between a working position and a retracted position to which itis taken just after the section of preform is seized.

The EP-A-0.284.242 document describes a machine of this type. In thisinstance it is a sequential type machine in which the rotation of thecarrousel is not continuous.

The machine described in this document has molding units that can slidevertically with respect to the carrousel between an upper workingposition and a lower retracted position. Immediately after a moldingunit has seized a section of preform, and until this unit has beenreleased below the extrusion head by rotation of the carrousel, themolding unit is moved toward its retracted position. This makes itpossible to prevent the preform from spilling over onto the upper faceof the mold during extrusion in a situation in which the preform orpreforms are continuously extruded.

The vertical sliding of the molding unit corresponds precisely to thedirection of extrusion of the preform. The magnitude of the movement ofthe molding unit should therefore correspond to at least the length ofpreform that is extruded during the time the blow-molding unit isimmobilized beneath the extrusion head. With this design, a free spacemust therefore necessary be provided beneath the working level of themolding units, to allow their retraction. This free space thereforesignificantly increases the total height of the machine.

Moreover, the slidable mounting of the molding units is particularlydifficult to accomplish satisfactorily. Excellent guidance must beprovided to ensure that the unit is perfectly stable, while stillallowing relatively fast movement at the time the unit is released.

SUMMARY OF THE INVENTION

A purpose of the invention, therefore, is to propose an improved designof a machine of the type described above, this design allowing machinesto be produced that have a high rate of production.

To that end, the invention proposes a machine of the type describedabove, characterized in that the molding unit is mounted on thecarrousel in order to be able to tilt around an appreciably horizontalaxis.

According to other characteristics of the invention:

the molding unit is articulated around an axis that is appreciablytangent to the path of the carrousel;

the axis of articulation is vertically off center with respect to thetop of the molding unit in the working position so that, at thebeginning of the tilting movement, the movement of the top of themolding unit has a horizontal component;

the part of the molding unit over which the extrusion head passes duringthe tilting movement has a chamfered shape;

the molding unit is mounted on a cradle that is articulated on thecarrousel by an inner radial side with respect to the axis of rotationof the carrousel;

both parts of the molding unit are movable with respect to each other ina direction that is appreciably radial with respect to the axis ofrotation of the carrousel;

the mold has at least two cavities that are offset along a directiontangential to the path of the carrousel, and the extrusion head (16) hasas many dies as the mold has cavities in order simultaneously to furnishthat many parallel preforms (15 a, 15 b) the separation of whichcorresponds appreciably to the offset of the cavities (30 a, 30 b);

the tilting of the molding unit from its working position to its tiltedposition is forced by drive means; and

the rotation of the carrousel around its axis is continuous.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear fromthe following detailed description, as well as from the attacheddrawings in which:

FIG. 1 is a diagrammatical view in axial cross section of a machineaccording to the invention;

FIGS. 2A to 2F and 3A to 3F are drawings illustrating by diagram therelative positions of a molding unit and of preforms extruded by theextrusion head at different moments following the seizing of thesections of preform and the closing of the molding unit, each positionbeing illustrated in side view (2A to 2F) and top view (3A to 3F).

DETAILED DESCRIPTION OF ILLUSTRATIVE, NON-LIMITING EMBODIMENTS

FIG. 1 represents the carrousel 10 of a machine for theextrusion/blow-molding of containers from thermoplastic material. Forexample, such a machine can be used to manufacture polyethylene bottles.

The carrousel 10 is movable in rotation around its axis A1 with respectto a fixed frame (not represented) of the machine. It carries a seriesof identical molding units 12 installed around its periphery.

The machine also has an extrusion unit 14 that ends in an extrusion head16 in which a die delivers one or more continuous tubular preforms 15 ofthermoplastic material that is still soft. In the example illustrated,the extrusion head 16 delivers two parallel preforms 15 a and 15 b thatflow vertically downward. In the machine according to the invention, theextrusion of the preforms is done continuously, that is, the speed offlow of the preforms is appreciably constant.

The extrusion head occupies a fixed position in the space in such a waythat, due to the rotation of the carrousel 10, each molding unit 12passes in turn under the extrusion head 16.

Indeed, in a known way each molding unit 12 has a two-part mold, eachmold part being carried by a support 18. The two supports 18 are movablewith respect to each other in a direction that, in the situationillustrated, is appreciably radial with respect to the axis A1 ofrotation of the carrousel 10.

As can be seen in the left portion of FIG. 1, in which a molding station12 is illustrated open to allow the ejection of a container 28, the twosupports 18 are mounted on a cradle 20 of the station 12 so as to beable to slide in radially, but in opposite directions. The opening andclosing movement of the supports 18 is controlled by a screw and nutsystem 22. This system is designed to cause the simultaneous movement inopposite directions of the two supports 18 with respect to the cradle20.

Thus, when the mold is opened and the molding unit 12 concerned passesbeneath the extrusion head 16, the mold can seize a section of preform15 that hangs below the head 16 and close again on the lower end of thepreform. In this instance, the mold seizes a section of each of the twopreforms 15 a and 15 b, each of these two sections being received into adifferent cavity 30 a, 30 b of the mold and the cavities 30 a, 30 bbeing in the shape of the container 28 to be manufactured. Generally, acutting device (not represented) is provided in order to easily separatethe section of preform that has just been seized by the mold from therest of the preform 15, which continues to be formed.

According to the invention, in order to prevent this preform thatcontinues to be formed from coming into contact with the upper face 24of the molding unit 12, each molding unit 12 is mounted on the carrousel10 in such a way as to be able to tilt around a horizontal axis Anbetween a working position and a retracted position.

The tilting axis An of each molding unit 12 is preferably appreciablyperpendicular to the radial plane of symmetry of the unit 12 inconsideration, said plane containing the axis A1 of the carrousel 10.

In the working position, the cradle 20 that carries the supports 18 ishorizontal so that the supports 18 can slide horizontally for theopening and closing of the mold. The result is that, when the moldingunit 12 is in the working position, the general plane of the faces incontact of the two parts of the mold, or the joint plane, is appreciablyvertical and perpendicular to a radius of the axis A1.

Preferably, the cradle 20 is articulated on the carrousel 10 by the sidethat is situated toward the interior. Thus, the axis An is radiallyoffset toward the interior and vertically downward with respect to theupper face of the molding unit. In this way, when the molding unit 12tilts downward around the axis An of its working position to itsretracted position, it can be seen that the upper face 24 of the moldingunit 12 follows a path that, at least at the beginning of the movement,has a vertical as well as a horizontal component.

In order to avoid the preform 15 that is descending from the extrusionhead 16, the upper face 24 of the molding unit 12 retracts downward andradially outward.

Moreover, it can be seen that the molding unit 12 does not have asymmetrical shape with respect to the joint plane of the mold. Indeed,the support 18, which is placed so that it is radially toward theinterior and the extrusion head 16 therefore passes over it when themolding unit 12 tips, has a bevel 26 that gives the top of the unit achamfered shape. Of course, this chamfered shape could also be achievedby a curved surface.

Represented in FIGS. 2A to 2F and 3A to 3F are different successiverelative positions of the preforms 15 and of the molding unit 12.

FIGS. 2A and 3A illustrate a theoretical position in which the cavitiesof the mold are each vertically aligned with the respective preform 15;the molding unit 12 is closed again and in the working position; and thesections of preform held inside the mold, which extend slightly abovethe upper face 24 of the molding unit, have just been separated from thepreforms 15 in process of formation by appropriate cutting tools.

This relative position of the different elements corresponds to an idealsituation and can only be precisely found in a sequential machine inwhich the carrousel is stopped periodically when a molding unit islocated precisely under the extrusion head in order to seize thepreform. In the case of a machine in continuous rotation, of the typeenvisaged by the applicant, slight offsets could be encountered withrespect to this ideal situation to optimize the operation of themachine. Thus the cutting of the preforms could be done slightly beforethe complete closing of the mold, the cut therefore occurring offsetwith respect to the exact moment the cavities pass directly below thepreforms.

Starting at that instant, different movements influence the relativeposition of the molding unit 12 and the preforms 15 a, 15 b. Thus, theextrusion head 16 from which the preforms flow is fixed, but the lengthof the preforms 15 a, 15 b increases linearly as a function of time. Themolding unit 12 is driven in continuous rotational movement around theaxis A1 of the carrousel, and according to the invention, it is drivenin a tilting movement around the axis An by pivoting its cradle 20.

FIGS. 2B, 3B, 2C and 3C clearly show the advantage of the horizontalclearance caused by the circular tilting movement of the molding unit.To be sure, in the absence of this horizontal movement the preform 15 athat has just been fed into the front cavity 30 a of the mold(considering the circular path of the mold around the axis A1) wouldpass directly over the rear cavity 30 b. Inside this cavity is a sectionof preform the upper end of which protrudes above the upper face of themolding unit. Also, to prevent any contact between the preform 15 a andthis protuberance, the molding unit must be made to withdraw veryquickly downward.

However, the beginning of the tilting movement of the molding unit isnecessarily at a relatively slow speed. Indeed, because of the mass ofthe molding unit to be put in motion, it cannot be made to acceleratevery quickly.

Also, it can be seen in FIG. 3C that, as a result of the horizontalcomponent of the tilting movement, the preform 15 a does not pass abovethe rear cavity 30 b.

FIGS. 2D, 3D, 2E, 3E show the importance of the chamfered shape of thetop of the molding unit. It can be seen that, if there were no bevel 26,that is, if the two supports 18 were completely symmetrical, thepreforms would risk coming into contact with the support 18 that issituated radially inside. The presence of the bevel 26 thus makes itpossible to limit the magnitude of tilting of the molding unit, and thusto limit the speed of tilting.

In the example illustrated, the tilting movement of the molding unit 12is controlled, in both directions, by an actuating cylinder. Obviously,however, any type of actuator can be used. In addition, a damper isprovided to dampen the tilting movement at the limit of travel both inthe retracted position (illustrated in FIGS. 2F and 3F) as well as whenit returns to the working position. Moreover, the molding unit is heldin the working position by a controlled lock coupled with a mechanicalstop.

As soon as a molding unit 12 has crossed the angular sector where theextrusion head 16 is located, it is moved to its working position forthe blow-molding operation. According to one preferred form ofembodiment, the blow-molding operation is performed with blow pins thatare moved vertically downward to penetrate at least partially inside theupper end of each of the sections of preform held in the mold. The useof blow pins rather than blow needles placed in the mold makes itpossible to produce containers that have a perfect sized neck.

Because of this, the blow-molding of the containers should be done withthe molding unit in a position such that the mold's cavities areoriented vertically.

Of course, the machine has as many blow-molding units 38 as moldingunits 12, and each of the blow-molding units 38 has two blow pins 40. Anupper plate of the carrousel carries the blow-molding units 38, and itcan be seen that they are radially movable with respect to the carrouselbetween an outer radial position, in which the pins 40 are directly overthe cavities of the respective molding unit, and a position retractedradially toward the interior. As can be seen in the right part of FIG.1, the blow pins must be radially retracted toward the interior whenthey pass into the angular sector in which the extrusion unit 14 islocated. Otherwise, the pins 40 would collide with the extrusion head16.

According to another feature of the machine according to the invention,each molding unit 12 is not articulated directly on the carrousel 10,but on a base 42 that is attached (removable) to the carrousel 10. Theactuating cylinder, the damper and the lock are also mounted on the base42 so that in the event of failure of a molding unit 12, the unit can beremoved very quickly simply by detaching the base from the carrousel 10.This makes it possible to limit the down time of the machine, which cancontinue to manufacture containers even with one less molding unit. Itis even possible to provide a standby blow-molding unit to immediatelyreplace the defective unit at least for the time required to repair it.

The provision of tilting molding units is particularly beneficialbecause of the very small increase in height that this involves for themachine. In addition, a pivot connection can easily be made between thecradle 20 and the base 42, which is particularly rigid, to ensure theperfect positioning of the molding unit 12 with respect to theblow-molding units 38 and the extrusion head 16.

Thus, the machine according to the invention makes it possible to expecthigh operating speeds while still being perfectly reliable.

What is claimed is:
 1. An extrusion, blow-molding machine comprising: aplurality of molding units carried by a carrousel which is rotatablearound a substantially vertical axis (A1), the molding units including atwo-part mold, both parts being movable with respect to each otherbetween an open position and a closed position; an extrusion head whichis placed above the carrousel in a specific angular position around thecarrousel's axis of rotation (A1), the molding units being controllableto be in an open position when the molding units are respectivelylocated below the extrusion head, and to be in a closed position afterhaving seized a section of a preform flowed from the extrusion head,wherein the molding units are mounted on the carrousel such that theyare respectively movable between a working position and a retractedposition, the retracted position being taken just after a section ofpreform is seized, and the molding units being mounted on the carrouselso as to be able to tilt around a substantially horizontal axis ofarticulation (An), and wherein the molding units are respectivelyarticulated around an axis (An) which is substantially tangent to a pathof the carrousel.
 2. The machine according to claim 1, wherein the axisof articulation (An) is vertically off center with respect to a top ofthe respective molding units in the working position so that, at thebeginning of the tilting movement, the movement of the top of themolding units has a horizontal component.
 3. The machine according toclaim 2, wherein a part of the respective molding units over which theextrusion head passes during the tilting movement has a chamfered shape.4. The machine according to claim 1, wherein the molding units arerespectively mounted on a cradle which is articulated on the carrouselby an inner radial side with respect to the axis of rotation (A1) of thecarrousel.
 5. The machine according to claim 1, wherein both parts ofthe molding units are movable with respect to each other in a directionthat is appreciably radial with respect to the axis of rotation (A1) ofthe carrousel.
 6. The machine according to claim 1, wherein the moldingunits respectively have at least two cavities which are offset along adirection tangential to the path of the carrousel, and wherein theextrusion head has as many dies as the molding units have cavities inorder to furnish simultaneously parallel preforms, the separation ofwhich corresponds appreciably to the offset of the cavities.
 7. Themachine according to claim 1, wherein the tilting of the molding unitsfrom their working positions to their tilted positions is forced bydrive means.
 8. The machine according to claim 1, wherein the rotationof the carrousel around its axis (A1) is continuous.
 9. The machineaccording to claim 1, wherein the molding units are configured such thatthey are positioned in the retracted position after the section of thepreform has been severed from a remaining amount of preform in theextrusion head.